Over the past twenty years, enteral nutrition has largely replaced parenteral nutrition as the preferred method of providing the metabolic needs of critically ill individuals. This is accomplished by administering specially formulated, liquid nutritional products through specially designed small bore enteral feeding tubes. While nutritional products used in enteral feeding vary in composition, they are formulated to satisfy the total nutritional needs of the patient.
Enteral feeding offers various advantages over parenteral feeding. Enteral feeding provides a more physiologic route of providing nutrition; by using the gut, it allows maintenance of mucosal barrier function, and permits healing of injured mucosa. Further, it is believed that enteral feeding prevents bacterial translocation through atrophic and injured mucosa, which is considered an important source of bacterial invasion in the pathogenesis of sepsis in some individuals. Additionally, the cost of enteral feeding, as well as the rate of associated complications, is lower than with parenteral feeding.
During the past twenty years, various advances have been made in the methods and equipment used in enteral feeding. Improvements have been made in the nutritional supplements themselves, as well as the devices by which the nutritional liquid is provided. Pump mechanisms have been developed for delivering the liquid nutrition, and these devices have been improved over the years.
Improvements have also been made in the feeding tubes utilized in enteral feeding. The use of various polymeric materials, such as polyurethane, in the manufacturing of feeding tubes has resulted in softer, and more flexible tubes, having reduced diameters. These features have resulted in greater patient comfort, and have enabled the feeding tubes to remain in position for longer periods of time, leading to increased acceptance of the use of feeding tubes.
Additionally, improvements in the distal end of the tubes have led to enhanced flow through the tube with fewer clogs. The use of weighted distal tips and stylets facilitates the nasogastric placement of lighter and less bulky tubes.
Although feeding tubes are sometimes passed orogastrically, most are currently passed nasogastrically. Generally, in placing a nasogastric feeding tube, the tube is first lubricated with a lubricant gel. The tube, along with a stylet, is then introduced into one of the nares, and advanced to the posterior pharynx. Once the tube is in the posterior pharynx, it is advanced through the esophagus so that the proximal end is at the nares or until enough tube has been passed to suggest gastric placement. The tube stylet is then removed. At any time, if insertion is felt to be outside of the alimentary tract, or if any firm resistance or patient discomfort is encountered, the tube is withdrawn, and reinsertion is attempted in either the same or the other nares. Placement into the stomach is verified by various physical examination maneuvers, aspirative tests, or radiograph. Once placement of the tube in the stomach or beyond has been verified, appropriate equipment is attached to the tube to deliver enteral nutrition.
Numerous problems may be encountered in the utilization of enteral feeding equipment and the delivery of liquid nutritional products. Among these problems are the ease and safety of various aspects of tube placement, issues of safety being the most important. Technical factors impact the ease and efficiency of tube placement and can affect patient comfort.
The risk of malplacement of feeding tubes is an important concern, and has been a major focus of medical literature describing complications of enteral feedings. Since the popularization of flexible, small bore feeding tubes, there have been more than 30 reports in the literature which describe aberrant placement of these tubes. The greatest occurrence of these reports concerns pulmonary malplacement. Feeding tubes are frequently malplaced into the lung due to the size and flexibility of the tubes, regardless of their use with stylets or guidewires. Risk factors for malplacement include endotracheal intubation, and a decreased sensorium.
Due to the risk of malplacement of feeding tubes, most institutions require verification of feeding tube placement prior to the initiation of feeding. The general view in the medical field is that physically examining patients by methods such as auscultation, and checking aspirate pH and myoelectric patterns are not adequate verification methods. The institutional policies of most hospitals therefore require that a widely-accepted and highly reliable test be performed to verify proper placement, wherein a radiograph which includes the thorax and upper abdomen is taken to ensure proper placement. Medical literature generally supports this view, and case reports on malplacement recommend this approach.
Compared to a feeding tube, a nasogastric (N-G) tube is considerably less difficult to place. An N-G tube is of relatively large diameter and less flexible, making it more difficult to pass into aberrant locations, such as a lung. Although reports of malplacement of N-G tubes exist, this is generally considered to be a very unusual occurrence.
An N-G tube is used diagnostically (e.g., pH testing of gastric fluid, evaluation of gastric contents in a GI hemorrhage) and therapeutically (e.g., decompression and removal of stomach contents, lavage, administration of medications). Nearly all patients in an Intensive Care Unit (ICU) will have an N-G tube placed for diagnostic and/or therapeutic reasons. Further, many patients on general medical and surgical wards have N-G tubes placed at some time during treatment.
In contrast to feeding tubes, verifying N-G tube placement is less difficult, given the caliber of the tube and enhanced ability to insufflate air and aspirate fluids (i.e., gastric). Radiographic verification is typically not necessary and not generally obtained to verify N-G tube placement. Rather, physical examination methods are typically used to verify placement. Moreover, the use of physical examination methods for N-G tube placement is supported by the literature.
In addition to safety concerns, technical difficulties may affect the ease and efficiency of feeding tube placement. For example, suitable sites to introduce naso-enteral feeding tubes may not be available, particularly in ICU patients. Additionally, structural variations in nares, posterior pharynx, and esophagus may likewise result in difficulties in the ease and efficiency of tube placement.
As indicated above, nearly all ICU patients have an N-G tube in place to facilitate management. Consequently, one nares remains for feeding tube placement. However, endotracheal tubes are often placed naso-tracheally, utilizing the available nares. Due to its large size, the placement of an endotracheal tube precludes passage of either an N-G tube or feeding tube through the same nares.
Although a feeding tube can be placed through a nares which already has an N-G tube in place, the placement is difficult for both practical and technical reasons. If an N-G tube is already in place, the friction created between the tubes makes it difficult to properly place a feeding tube in the same nares. Moreover, an N-G tube is larger and less flexible than a feeding tube, and is, therefore, generally easier to manipulate. Consequently, if a feeding tube is to be placed in the same nares as an N-G tube, the generally accepted procedure is to place the feeding tube first, then place the N-G tube, even though this may require that an N-G tube, which is already in place, be removed to allow this order of placement. Inasmuch as there is usually some delay in feeding tube placement once a patient enters an ICU, an N-G tube is generally already in place when the feeding tube is placed.
Even when a nares is available solely for feeding tube placement, certain disadvantages are associated with the use of this second site. Patients may have anatomic variations in nares, posterior pharynx, and esophageal anatomy. While these variations may not be troublesome with regard to the placement of a larger, less flexible N-G tube, they may cause considerable problems or preclude passing a flexible feeding tube.
Additionally, placement of a second tube in a new site, i.e., the second nares, raises issues of patient comfort. The patient must endure the discomfort associated with the process of insertion and manipulation of a second free-standing tube.
Finally, the risks associated with the placement of a second free-standing tube in a second site is compounded in patients with hematologic abnormalities, including coagulopathies, and platelet deficiencies.
The technical difficulties outlined above impact not only patient comfort and safety, but also physician utilization of enteral feeding. Difficulty in implementing naso-enteral feeding may result in delays in implementation of feeding, the use of alternate nutritional modalities that are more dangerous and expensive, such as parenternal nutrition, or foregoing nutritional support completely.